Linux Commands

To see Ip address of the machine

• ip addr show :Shows all the interfaces ip
• ip -4 addr show: Show only ipv4 address
• ifconfig: Same as ip addr show but it needs net tools to show ip address.

Systemctl commands

• sudo systemctl start servicename: To start the service
• sudo systemctl stop servicename: To stop the service
• sudo systemctl enable servicename: To enable the service
• sudo systemctl disable servicename: To disable the service
• sudo systemctl is-active servicename: To see whether the service is active or not
• Service command:
  • [service] [service_name] [command]
    • service apache2 status
  • commands in service can be ie;start, restart, reload, status, stop

Change directory [cd]

Command	Description
cd /filename	To change the directory to the certain file name Ex: cd /opt, cd /tmp, cd /var
cd ../	To go 1 step back from current position
cd ../../	To go 2 step back from current position
cd –	To go to the recently used directory
cd ~	To go to the home directory
sudo -i	To go to the root user home directory Ex: root@jenkins:~#

Listing command [ls]

Command	Description
ls	Simply list all the contents available in the directory
ls -a	List all the files including hidden files
ls -l	Long list all the contents of the directory
ls -al	Long list all the contents of the directory including hidden files
ls -hl	Long list all the contents of the directory in human readable form
ls -lr	Long list all the contents of the directory in reverse order
ls -lu	Long list all the contents of the directory based on the recently accessed files and directories at the top
ls -i	Long list all the contents of the directory and also show the inode number
Note:	while long listing if the file starts with these symbols it determines the file type – : text file d : directory . : hidden files l : linked files

Basic commands

• date: To see the current date
• timedatectl: To print date, region all the details
  • sudo timedatectl set-ntp true: to set ntp to true in case of sync issue
  • sudo timedatectl set-timezone Asia/Kathmandu: To change timezone
• whoami: Print username
• who: Print who have accessed the machine
• hostname: To see the hostname
• sudo hostnamectl set-hostname hostname_you_want_to_write: To change the hostname
• cat filename: Print the file content
  • cat -n filename: To print the content with line number
  • cat filename1 filename2: TO print multiple files
• tac filename: Concatenate and display file content in reverse
  • Shows the content of file that is at top in bottom.
• uniq – Report or omit repeated lines
  • uniq filename
• stat – Display file or file system status
  • stat filename
• clear: To clear the screen
• mkdir dirname: To create the directory
  • mkdir dirname{1..5} : It will create 5 directories
• passwd: To change the password of the machine
• file filename/dirname: To see file type of any file
• wc filename : To see the word count of any files
  • Ex: wc cd/var/log/syslog ;Very powerful log file that has all the logs of system
• history: To see all the past commands that we have ran in the machine.
  • !136: To run the 136 number command
  • !!: To run the recently used command
• df -h: Display the result of disk utilization
  • df -hi: used to display filesystem inode usage information in a human-readable format.
• free -m : Shows memory utilization data
• **stat filename**: Used to display detailed information about a file or filesystem, including metadata like permissions, size, ownership, timestamps, and inode details.
• which apt: To see pat path
• which $SHELL: To see the used shell
• echo $?: To check status of last command
  • 0 for success
  • 1 if command fails
• tree: TO see output in tree like structure
  • tree -a: To see hidden files also

Copy command

• cp sourcefile targetfile
  • Ex: cd /home/user/doc/report.txt /home/usr/backup/destination
• cp -i: To get prompt while copying
• cp -r: To recursively copy [means all in the directory]
  • Ex: cp -r dir1/* dir2/*

Move command

• mv file1 file2: To rename the file and also move the contents of the file
• mv -i file1 file2: To get prompt while moving contents of the file
• mv dir* dir1: To move all the contents of the directory to dir1.
• mv dir1 dir2: Moves the dir 1 to the dir2.
• NOTE: While moving contents between the files we don’t need to specify -r flag. By default it will move the contents recursively.

Remove Command

• rm filename: To remove the file
• rm -i filename: To get prompt while removing the file
• rm -r dirname: To remove the directory we need -r flag
• rm -rf dirname: To remove the directory forcefully
• rm -d dirname: To remove the directory
• rmdir: To remove the directory

To get help and see suggestion in linux

• tab: It will auto complete the word when you are accessing some directories or accessing some files.
• double tab: Shows all the files and directories in current path
• info command_name: To see detailed information of any command
  • info ls
  • info cat
• command –help: To see options we can use with that command.
  • grep –help
  • touch –help
• man command: To see manual page of any command.
  • man cat
• If we forgot the command but we want to do certain task then we can write the apropos task_name and if we show all related to that task.
  • Example: apropos copy ;Shows all commands related to the copy
  • apropos move ; Shows all the commands related to move

To view/print contents of file

Head

• Print the data from top
  • Example:
    • head syslog: Print 10 lines from the top ie;by default
    • head -n 20 syslog: Print 20 lines from the top. We can define how many lines we want to print by using -n flag.
  • NOTE:
    • Logs files cd /var/log
    • cloud.init.log: Scripts running during bootstrap output is in this directory.
    • dpkg.log: Logs during the package installation
    • sys.log: Details of all the services logs {Very powerful log file}

Tail

• To print the data from the bottom.
  • Example:
    • tail syslog: By default it will print 10 lines.
    • tail -n 20 syslog: It will print 20 lines
    • tail -f syslog: To see real time log

More

• To read contents line by line and page by pafe
  • Press Enter to move to the next line
  • Press Space to move to the next page

Less

• Similar to the move but is more powerful
  • d: Move to next page
  • b: move to the previoys page
  • /text_you_want_to _look_for : Search anything through the any file

Find

• To find anything with the name, type, user and group
• syntax:
  • sudo find / -name filename:→ find file named test1.txt in root dir and subdirectories
  • find . -name dpkg.log: → find all files whose name is dpkg.log in current directory
    • -name:To search based on the name
    • -inum: To search based on inode number
    • -type: To search based on the type
    • -user : For files whose owner is a particular user
    • -group : For files belonging to particular group
  • Example:
    • find / -name dpkg.log
    • find /etc/ -group shadow -ls
    • find / -type l -ls → find files with symbolic link
    • find / -type d -name Pictures
  • find . -type d -name “terraform“: Took for directory
    • If you don’t know full name you can use “*terraform*” also.
  • NOTE:
    • / Absolute path: It will start search after going to the home.
    • . Relative path: It will start looking for the file from the current directory

Locate

• The locate command works reading contents from the database.
• Find files by name
  • apt-get install mlocate
• The db must be updated
  • sudo updatedb
• Example:
  • locate dpkg.log
  • locate -i readme.md

Grep

Tool to search string in a file. Basically are a character or group of characters that
represents certain things in a string. We can look for anything in the file using this command.

Commands:

• grep -n: Print content along with the line number.
• grep name test.txt: Print line having name {case sensitive}.
• grep -i name filename: To ignore the case. Not case sensitive.
• grep ^name: To search for the line which word startswith with name.
• grep name$: To search for ends with word.
• grep [nN]ame: Look for both case for n word.ie: name and Name also.
• grep [0-9][0-9]$: Look for the line that have at least two numerical value at the end. Here [0-9][0-9] determines the total number of the words.
• grep -v hello word.txt: Except hello word it will print all and ignore the hello.

Sed [Stream Editor]

sed stands for stream editor, which is used to search a word in the file and
replace it with the word required to be in the output.

Also used to look for specific lines from the file

sed -n ‘3p’ filename.txt # Show 3rd line

syntax: sed -e ‘s/find this/replace with this/g’ /etc/passwd

Here:

• Here -e indicates giving some expression.
• s indicates find.
• Find this, contents to be replaced.
• Replace with this, contents that replace the existing one.
• g indicates global search and replace

Example:

• sed -e ‘s/ansible/devops/g’ /etc/passwd
• sed -n ‘2p’ /etc/passwd
  • Here -n flag (silent/negation) ignores all the non important lines. p is
    for printing and 2 is for the 2nd line.
• sed -n ‘$p’ /etc/passwd
  • Print last line
• sed -n ‘3,6!p’ /etc/passwd
  • Print all lines except 3rd to 6th line
• sed -i ‘s/Suryaraj/raj/g’ abc.txt
  • -i option allows to write on the same file
• sed -e ‘s/…../………./g’ word.txt >newtmp.txt
  • Modify the word.txt file and redirect the output to the newtmp.txt
• sudo -u www-data -i ‘s/database_name_here/wordpress/’ /srv/www/wordpress/wp-configuration
  • Here -u :As the user www-data
  • /srv/www/wordpress/wp-configuration: Path to the file
• Note: sed -i is a bit dangerous than sed -e
  so instead of original file always check by making another file or by creting backup.

Cut

Helps to extract data column by column

• Examples:
• cut -c1 /etc/passwd
  • To print the 1st character of every row of the 1st column.
• cut -c1-5 /etc/passwd
  • To print the 1st to 5th character.
• cut -d ‘:’ -f1 /etc/passwd
  • Here -d is the delimiter(breaks) and f1 represents field1 column 1.
• cut -d ‘:’ -f2-3 /etc/passwd
  • Here f2-3 represents the fields 2 to field 3.
• To delimit spaces and print the field
  • cut -d ” ” -f1 filename
  • cut -d -f filename(where d stands for delimiter eg. :, ” ” f stands for field)

Here Delimeter means fields/colums are seperated by special character that is known as delimter.

AWK

AWK is a family of tools that are primarily used for processing texts files.
The most basic use of AWK is parsing the files and generating reports.
Syntax: awk ‘/search pattern/ {Actions}’ file

• Search pattern in a regular expression.
• Actions – Statements to be performed.
  • Several patterns & actions are possible in AWK.
• File – Input file
  • Single quotes around the program is to avoid shell not to interpret any
    of its special characters.
    ‘Print only specific field’. AWK has a number of built-in variables. For each record i.e line, it splits the record delimited by whitespace character by default & it stores in the $n variables.
    E.g If the line has 4 words, it will be stored in $1, $2, $3, $4.
    $0 represents the whole line.
    awk -F ‘:’ ‘{print $1}’ /etc/passwd , df -h | awk -F ” ” ‘{print $2}’

VIM

VI: Visual display editor
VIM: Visual display Improved

TO install:
sudo yum install vim
sudo apt-get install vim
VIM Mainly have three modes. They are

Normal mode(command mode)	This mode provides you an efficient way navigate and manipulate text. ESC to go to the normal mode
Insert mode	you can write text as in any normal editors Press I to go to the insert mode
Extended normal mode(command mode)	extended mode provides the ability to save, quit functionalities : this is extended mode.

Navigation

Basic Navigation	h : move to the left j : move to the down k : move to the up l : move to the right
Word by word navigation	w : moves to the start of next word in a sentence e : moves to the end of the word b : moves to the beginning of the word [Reverse order] nw: To skip multiple words [forward order, 3w,5w] nb: To skip multiple words [Reverse order]
Finding a character.	f : for next occurrence of a character. F : for the previous occurrence of the character. Note: you can combine f with the number for multiple occurrence of a character.
Go to the start or end of a sentence	0 : for the beginning of the sentence. $ : for the end of the sentence.
Finding the word under cursor	*: for the next occurrence of the word #: for the previous occurrence of the word.
To move courser in whole file	gg: To move the cursor to the beginning of the file G: To move the cursor to the end of the file 2G: To go to the line two
To search in the file	/ followed_by_text. after that press n for next And N for the previous
Insert new line.	o: Below O: Above
Removing a character	x : deletes the character under cursor X : deletes the character to the left of the cursor
Replacing character under cursor	press r
Delete command	d is the delete command dw deletes the first word on the right side of the cursor dd deletes a line ndd delete n lines d2e removes two words to the right of the cursor
Undo the changes	u to undo last change(word) shift+u undo last change(sentence) Ctrl + r to redo
Copy and Paste	yy to copy a line nyy: to copy n lines p to past a line below shift+p to paste a line above
Visual Mode	Visual mode is the another mode of VIM editor In this mode you can select text using the movement keys before deciding any actions. Go to visual mode by pressing v Select word with e After selecting you can remove it by pressing d

Extended mode

• ESC+:w : to save
• ESC+:q : to quit
• ESC+wq : Save and quit
• ESC+w! : Save forcefully
• ESC+q! : Quit forcefully
• ESC+wq! : Save and Quit forcefully
• ESC+:x : To save and quit
• ESC+:2(n) : Go to line no 2o or n
• ESC+:se nu : Set line number
• ESC+:se nonu : Remove line number
• / search word in a file
• :help for vim help
• Note:
  • vim +7 test.txt: Go to the line no 7 when opening in text editor
  • %s/Look_for/replace_with: Look for the certain text and replace it Only replace the first occureance.
  • %s/Look_for/replace_with/g: Look for the certain text and replace it globally.

Input/Output redirection

Redirection means we can redirect the standard output, standard errors and standard input to any files and also can change the direction of input/output from terminal to files.
Standard Input

1. wc
   → gives no. of lines, words and no. of characters.
2. wc
   → Waits for the standard input if no argument is passed. Give some standard
   input and press ctrl+d to exit and see the output. If you provide a file name, it operates on filename. If you do not give the file name, it operates on standard input.
   Standard output
3. ls
4. whoami
5. date
   Standard Errors
6. $ lss
   → command not found
7. $ ls /binn
   → No such file or directory
8. $ cat /etc/shadow
   → permission denied

Input redirection

The < sign is used to redirect the standard input that we pass to any file.
syntax:
command << delimeter
content or commands
that you want to redirect.
delimiter
Example:
wc -l << EOF
This is a simple program
EOF

• tee: overwrites the file
• tee -a: append to the file

  • tee -a filename <<EOF
    We are adding some content in
    the file filename.
    EOF

    This will add the content to the file filename.

Output redirection

This is used to redirect standard output or error to any files.
1>: Redirect only standard output to the file
2>: Redirect only error to the file
&>: Redirect all output and error to the file
Example:
1>/dev/null : This command will redirect standard output to the file /dev/null which is like a blackhole.

who > user.txt :Here the output of who is redirected to the user.txt instead of terminal. It overwrites the content.

Append
$ date >> command.out –> Appends the new contents in old contents, does not replace.
$ whoami >> command.out
cat command.out

Note:
>:Used to rewrite or redirect only
>>: Used to overwrite the content

Standard error output

$ lss 2> error.out –> standard error output redirected into the file.
To append:
$ lss /binn 2>> error.out –> appends
$ cat error.out

To download using links

• wget url: To download remotely with link
• curl -o URL : To download remotely and select directory for download
  • curl -k url : For insecure website
  • curl localhost: To curl local host

Apache web server

1. Difference between Apache web server and nginx web server
2. To install apache2
3. Commands
4. Apache2 configuration overview
5. To load a website in apache2

Vagrant

1. Vagrant Architecture
2. To setup vagrant VM
3. Commands
4. Other Configurations

Shell Scripting

1. Writing our first script
2. Variable
3. To take input from user we use
4. Positional Argument
5. Command substitute
6. If
7. For
8. While

Linux commands[2]

1. Linux Links
   1. Soft links
   2. Hard Link
   3. Inode
2. Packet Management
   1. APT [Advanced Packaging Tool]
   2. APT-CACHE
   3. Aptitude
   4. dpkg
3. Users and Groups
   1. Types of users
   2. Files related to users and groups
   3. User Commands
   4. Group commands
4. File permissions
   1. Changing permissions
   2. Changing ownership of file
   3. Changing group ownership for file/dir
   4. Managing file and group ownership simultaneously
   5. Special permission
      1. Sticky-bit
      2. SUID-bit
      3. SGID Bit
5. Archiving and Compressing
   1. Archiving:
   2. Compression
6. Sudo
7. Processes
   1. top
   2. Process status(ps)

Linux Introduction

1. Overview
   1. Operating System
   2. Principles
   3. Why Linux?
2. Architecture
3. Linux Terminology
   1. Linux Kernel
   2. Linux Distribution
   3. Linux BootLoader
   4. Linux Service
   5. Linux File System
   6. Linux X Windows System
   7. Linux Desktop Environment
   8. Linux Command Line
   9. Linux Shell
   10. Linux Distros
4. Linux File Structure
   1. / – Root
   2. /bin – User Binaries.
   3. /sbin – System Binaries
   4. /etc – Configuration Files
   5. /dev – Device Files
   6. /proc – Process Information
   7. /var – Variable Files
   8. /tmp – Temporary Files
   9. /usr – User Programs
   10. /home – Home Directories
   11. /boot – Boot Loader Files
   12. /lib – System Libraries
   13. /opt – Optional Add-on Applications
   14. /mnt – Mount Directory
   15. /media – Removable Media Devices
   16. /srv – Service Data
5. Interface and logging in via terminal
   1. Remote login via ssh
6. Linux File system